Timehop is a reminiscence app for those that don’t already have Facebook. It pulls photos from your social media streams to remind you what you were up to a year ago, 5 years, 10 years ago etc. There’s nothing quite like a photo to trigger memories of a certain period of life. Sometimes I wonder if I would even be able to recall a tiny fraction of my life’s events in a world before photography. It’s usually the case that if a life event is deemed worthy of being captured in a photograph, then seeing it again will encourage a positive frame of mind. Only yesterday I overheard a relevant discussion between a pair of colleagues in my local supermarket. One showed the other a photograph of a family trip to Jamaica on his smartphone and the other murmured: “I love looking at old photographs, it’s just the best.”
The damage that Alzheimer’s disease does to the brain regions that support retrieval of autobiographical memories can eventually extinguish a person’s very sense of self, more often than not, the abolition of recollections from early on in life doesn’t occur until the end of the process. For most of our lives, from developing a sense of self in infancy, to ultimately losing it once and for all, our sense of who we are follows an arc that seems to be wholly dependent on the accumulation of most poignant memories, often revolving around novel and emotionally stimulating experiences. They are a reference point from which we get our sense of who we are. They are physically manifested in extra synaptic connections in neural circuitry distributed all across the brain, far beyond the hippocampus famed for it’s involvement in the creation and retrieval of memories. This brain blog is about the cues that can trigger recollection of our life’s key experiences that are so important in defining to ourselves who we are.
At first a newborn infant has no sense of self. At this stage, even the very senses it uses to understand the world around it have yet to develop to the point where reliable information can be gleaned regarding what’s out there. The brain first must be exposed to a vast torrent of sensory experiences that help to shape and mature brain areas that crunch the information coming in through the various sensory systems during early brain development. The capacity to actively explore the environment further enhances these memories for our early experiences, until sufficient experimentation of cause and effect results, miraculously, at some point during the second year of life (usually between 15 and 24 months) in the classic signs of awareness of selfhood. Infants recognise that the reflection in a mirror is themselves, as evidenced by attempts to wipe off a coloured mark that might have been surreptitiously smeared on their cheek.
Our sense of self develops in childhood as we experience more and more significant, emotionally affecting life episodes, which are each logged away deep somewhere in the recesses of our mind. Foods and people we like and dislike. Places in which we experienced pleasures and pains. Circumstances associated with unpleasant emotions associated with hunger, cold and threats, others that predicted feelings of comfort, excitement and laughter. Life’s surprises and first time encounters dominate those memories that are most easily brought to mind.
Once we look back on childhood from the perspective of a fully-grown adult some interesting quirks of memory start to become evident. First is that memories from our earliest years of life are wiped. This childhood amnesia manifests as a complete inability to recall much of what happened to us before the age of three or four. Perhaps the odd fleeting memory of one or two key events at the age of four at best, but nothing from the ages of 0-3 years old.
The sense of smell has an astonishing capacity to remind us of early childhood memories. This can be accounted for by the fact that, of all our senses, the olfactory system is the only one that plugs directly into the brain’s cortex without first filtering through the thalamus. The thalamus is the brain’s major junction box through which the senses of vision, hearing, touch and taste are required to interface before being shuttled on for further processing at various dedicated patches of the crinkly outer surface of brain tissue. There are two major sites at which the sense of smell is generated according to the different types of gaseous chemicals detected deep inside the nostrils by hundreds of different types of olfactory receptor. One is on the underside of the frontal cortex and another on the medial (inward-facing) temporal lobes. The temporal lobes also house the hippocampus (fundamental to the creation of new memories) and the amygdala (critical for the production of emotions) perhaps explaining why scents tend to produce a powerfully emotional sense of reminiscence, typically evoking memories from before the age of 10.
The reminiscence bump describes the observation that, further back than their most recent experiences, adults over the age of fifty are most likely to recall experiences from late adolescence and early adulthood (15-30 years old). Whether cues used to elicit important memories are pictures or individual words, the majority of autobiographical episodes that pop into our mind tend to come from this period of life. A period in which significant events mold our character and help to form our adult self.